Development of low- lossAg-sheathed superconducting tapes based on electromagnetic design and their application to AC power cables

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Studies on development of low-loss Ag-sheathed superconducting tapes based on electromagnetic design and their application to AC power cables have been conducted for three years between fiscal 2005 and 2007. Main results through the study am summarized as follows:(1) Construction of AC loss measurement systemWe constructed the measuring system to obtain the AC losses generating in superconducting tape under AC operation, in passing through AC transport current and AC external magnetic fields at arbitrary directions to tape surface. Using this, we can obtain total values of AC losses obtained by a sum of AC transport losses and AC magnetization losses in the tapes and/or wires, while changing frequency, transport current amplitude and magnetic field amplitude.(1) Fabrication and characterization of Ag-sheathed high-Tc superconductiong tapes with interfilamentary resistive barriersWe successfully fabricated Ag-sheathed high-Tc superconducting tapes with interflamaaary resistive barriers … More and investigated their electromagnetic properties toward applications to electric power cables. We used two methods for banier introduction in tape fabrication. The one is the coating method using paste of resistive barriers and another the inner oxidization method using metals with nice mechanical properties. In particular the tape fabrication using mixture of Ca_2CuO_3 powder and 30 wt%Bi2212 powder as barrier materials produces Ag-sheathed tapes on the order of several meter lengths, which have considerable nice and homogeneous J,(77K, OT) distribution well above 10^4 A/cm2 (1.8 x 10^4A/cm2 at maximum). In addition, this barrier introduction causes several-times enhancement in transverse resistively and lowers the AC losses up to 1/3 compared to the tapes without barrier introduction.(2) Electric fields andAC losses for cylindrical conductor cables composed of Ag-sheathed superconducting tapesWe elucidate the electric-field distribution near cylindrical conductor cables composed of Ag-sheathed superconducting tapes based on the electromagnetic theory, which plays an important role in the error estimation for AC losses from measurements. The electric field under AC operation shows complicated variations in the vicinity of cables depending upon the cable structures and it becomes nearly constant in going away from the tape surface by about tape width. The result shows that AC loss measurements for cable conductors should be made at the distance far from the tape surface by at least tape width Less